Super-Resolution Track-Density Imaging Reveals Fine Anatomical Features in Tree Shrew Primary Visual Cortex and Hippocampus

Diffusion-weighted magnetic resonance imaging（d MRI） is widely used to study white and gray matter（GM） micro-organization and structural connectivity in the brain. Super-resolution track-density imaging（TDI） is an image reconstruction method for d MRI data, which is capable of providing spatial resolution beyond the acquired data, as well as novel and meaningful anatomical contrast that cannot be obtained with conventional reconstruction methods. TDI has been used to reveal anatomical features in human and animal brains. In this study, we used short track TDI（st TDI）, a variation of TDI with enhanced contrast for GM structures, to reconstruct directionencoded color maps of fixed tree shrew brain. The results were compared with those obtained with the traditional diffusion tensor imaging（DTI） method. We demonstrated that fine microstructures in the tree shrew brain, such as Baillarger bands in the primary visual cortex and the longitudinal component of the mossy fibers within the hippocampal CA3 subfield, were observable with st TDI,but not with DTI reconstructions from the same d MRI data.The possible mechanisms underlying the enhanced GM contrast are discussed.